Fabrication of electronic circuit elements using liquid deposition techniques is of profound interest as such techniques provide potentially low-cost alternatives to conventional mainstream amorphous silicon technologies for electronic applications such as thin film transistors (TFTs), light-emitting diodes (LEDs), RFID tags, photovoltaics, and the like. However the deposition and/or patterning of functional electrodes, pixel pads, and conductive traces, lines and tracks which meet the conductivity, processing, and cost requirements for practical applications have been a great challenge.
Fabrication of electronic circuit elements using silver paste based on thick film technology, in which the paste is comprised of silver flakes dispersed in polymer binder, is known.
There are drawbacks with the use of silver flakes based on thick film technology. First, as electronic devices become smaller and smaller, high resolution conductive traces are often required. Due to the size of silver flakes (10 to 100 micrometers), high resolution traces (for example of less than 125 micrometers) are very difficult to achieve using the paste. Second, due to the relatively low conductivity of the paste, low resistance is often achieved by depositing a very thick layer (for example of greater than 10 micrometers). As a result, a large amount silver flake material has to be used. As silver prices continue to increase dramatically, the silver pastes with silver flakes become uneconomic.
U.S. Patent Application Publication No. 2011/0135808, incorporated herein by reference in its entirety, describes a method of forming conductive features on a substrate by reacting a metal compound with a reducing agent in the presence of a stabilizer in a reaction mixture comprising the metal compound, the reducing agent, and the stabilizer, wherein the reaction mixture is substantially free of solvent, to form a plurality of metal nanoparticles with molecules of the stabilizer on the surface of the metal nanoparticles. After isolating the plurality of metal nanoparticles, a liquid composition that includes a polymeric binder, a liquid and the plurality of metal nanoparticles with molecules of the stabilizer on the surface of the metal nanoparticles is deposited on a substrate by a liquid deposition technique to form a deposited composition. The deposited composition is then heated to form conductive features on the substrate.
While currently available silver pastes for preparing conductive elements for electronic devices are suitable for their intended purposes, there remains a need for improved pastes capable of forming high resolution traces and having high conductivity, that are desirably also be more economical.